The present invention relates to hydrocarbon catalytic cracking catalyst compositions and in particular relates to catalyst compositions which exhibit high metal tolerance, maintain high catalytic activity and gasoline selectivity for a long period of time and can depress hydrogen and coke formation to a low level when used in catalytic cracking of heavy oil containing large amounts of heavy metals such as vanadium, nickel, iron, copper and the like and a method therefor.
Catalytic cracking of hydrocarbon originally aims at the production of gasoline. Therefore, catalysts used therefor are naturally demanded to exhibit high catalytic activity and gasoline selectivity, and further, metal tolerance.
In recent years, it is becoming necessary, with deterioration of the oil situation, to employ low grade heavy oils, typically residual oils, containing large amounts of heavy metals such as vanadium, nickel, iron, copper and the like as a feed stock for catalytic cracking. This attaches more importance to metal tolerance of catalytic cracking catalysts.
In catalytic cracking of heavy oils, the cracking activity and gasoline selectivity of the catalyst used therefor generally deteriorate more or less because of the deposit of metallic contaminants contained in feed oils on the catalyst. In view of this, it is customary that the usual commercially used catalytic cracking catalysts, exemplarily catalytic cracking catalysts comprising zeolite dispersed in porous inorganic oxide matrices, have such metal tolerance that they can maintain a satisfactory catalytic ability even when a certain degree of metals deposit thereon. However, in catalytic cracking of the above mentioned low grade heavy oils using the catalyst of this sort, it is impossible to achieve the primary object of catalytic cracking because a large amount of metallic contaminants admixed with said oils deposit on the catalyst whereby a dehydrogenation reaction is accelerated, formation of hydrogen and coke is increased, and further, the crystal structure of zeolite is apt to be destroyed.
Accordingly, when subjecting the low grade heavy oils containing a large amount of metallic contaminants to catalytic cracking, there have usually been employed the procedure of suppressing the deposited amount of metal per catalyst particle by increasing the amount of catalyst used, the procedure of preventing the deterioration of the catalytic activity caused by metal deposit by adding an antimony compound in the feed oil, or the like. However, these operational countermeasures can never be recommended because the running cost increases. On the other hand, as the countermeasure from the catalytic ability there has been known the one which comprises increasing the amount of zeolite to be dispersed in the catalyst in comparison with that in the normal catalytic cracking catalyst, and further, U.S. Pat. No. 4,430,199 discloses a catalytic cracking catalyst improved in metals tolerance by incorporating a phosphorus compound in a zeolite-containing catalytic cracking catalyst. Still further, U.S. Pat. No. 4,228,036 discloses a catalytic cracking catalyst prepared by dispersing zeolite in a matrix comprising alumina-aluminum phosphate-silica.
In addition, U.S. Pat. No. 3,711,422 describes that the addition of an antimony compound to a catalytic cracking catalyst deactivates the metallic contaminants deposited on said catalyst, and U.S. Pat. No. 4,183,803 describes a process for passivating metallic contaminants by contacting the metallic contaminants-deposited catalyst with a compound of antimony, bismuth, phosphorus or the like.
In addition, U.S. Pat. No. 4,222,896 proposes a catalyst comprising a MgO-Al.sub.2 O.sub.3 -AlPO.sub.4 matrix composited with zeolite, and Japanese Laid Open Patent Application 150539/1984 proposes a catalyst comprising an alumina-magnesia matrix composited with zeolite, respectively. Of the usual catalytic cracking catalysts developed in order to improve metals tolerance thereof, the catalyst whose zeolite content has been increased can never be made a commercially attractive one. The catalyst containing a phosphorus component with or without antimony, bismuth, magnesium and the like is not necessarily satisfactory in metal tolerance. The phosphorus component and the above mentioned other metals are surely attributable to improvement in metals tolerance, but it is conjectured that the usual catalysts, wherein the phosphorus component and other metallic components are dispersed uniformly throughout the catalysts, can never obtain satisfactory results when too much metal deposits thereon because the metal tolerance of the catalysts deteriorates.
We have found that when an alumina-containing catalytic cracking catalyst is utilized for catalytic cracking of hydrocarbon oils and vanadium is deposited thereon, and when the spent catalyst is analyzed by means of an X-ray microanalyzer, the distribution of the deposited vanadium well corresponds to that of alumina. This fact suggests that when alumina is allowed to be present, taking the form of small particles or lumps, in the catalytic cracking catalyst, metallic contaminants can be deposited preferentially on these small particles or lumps of alumina.